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Detailed Analysis of the Hydrogen Sulfide Production Step in a Sulfur-Sulfur Thermochemical Water Splitting Cycle

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Detailed Analysis of the Hydrogen Sulfide Production Step in a Sulfur-Sulfur Thermochemical Water Splitting Cycle 1 AN ABSTRACT OF THE DISSERTATION OF Kevin R. Caple for the degree of Doctor of Philosophy in Chemical Engineering presented on January 24, 2014. Title: Detailed Analysis of the Hydrogen Sulfide Production Step in a Sulfur-Sulfur Thermochemical Water Splitting Cycle Abstract approved: _________________________________________ Alexandre F.T. Yokochi The production of hydrogen has been one of the most heavily studied, energy related fields over the past half century, yet few methods are commercially or economically viable and none are currently sustainable. Of those aiming at the sustainable production of hydrogen using renewable resources, perhaps the most widely studied are those attempting to thermochemically split water via various chemical intermediates. These provide an attractive conceptual alternative to other methods due to lower energy input requirements and to the production of the targeted hydrogen and oxygen in separate reaction steps. One of the most widely studied thermochemical cycles is the Sulfur-Iodine cycle, the development of which has recently slowed due to the difficulty in the separation of hydrogen iodine from a hydrogen iodide-iodine-water azeotrope, material compatibility issues, and the perceived need use large amounts of iodine in the process. A modification of the Sulfur-Iodine thermochemical cycle that attempts to avoid those issues along with mitigating the need to process large amounts of water in the cycle was developed, in a cycle we describe as the Sulfur-Sulfur cycle. This new thermochemical cycle can be summarized by the reaction sequence shown below. ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (( )) ( ) Previous work in our group demonstrated the viability of implementing the cycle’s low temperature reactions (the first reaction pair, which we call the Bunsen reaction and the Hydrogen Sulfide Production (HSP) reactions) in ionic liquids, which removes the need to process large amounts of water and iodine in the reaction sequence, and minimizes the material compatibility issues, and also demonstrated the feasibility of stream reforming hydrogen sulfide. The present work focuses on an exergetic analysis of the Sulfur-Sulfur cycle, the careful determination of reaction kinetics for the HSP reaction, and developing a model of the kinetics of the low temperature reactions. The exergetic analysis was carried out based on the published therrmochemical parameters for the species involved. The analysis showed that the maximum theoretical exergetic efficiency of the Sulfur-Sulfur cycle is nearly 70% with a strong dependence on the reaction temperature of the low temperature reactions. The kinetics of the Bunsen and HSP were investigated through iodine colorimetery and the effect of water was determined. This kinetic data was used for the development of a predictive kinetic model that could accurately monitor the progression of iodine through the reaction system. The work showed that the Bunsen reaction is very fast with an activation energy ( ) of 92.83 kJ/mol and a pre- -1 exponential factor ( ) of 7.65E+14 min , while for the HSP reaction, they were determined to be 117.09 kJ/mole and 7.73E+16 min-1. Integration of these two reactions into a single differential model based on iodine concentration fit the experimental profile extremely well The effect of including a Lewis base other than water in the reaction mixture yielded promising results that warrant future development. Specifically, the rates of both the Bunsen and HSP reactions increased with an increase in the pKb of the added Lewis base. A local protocol to recycle the ionic liquid, enabling it to be reused in new experiments, was successfully developed. When the recycled ionic liquid is employed, effects similar to those found through the inclusion of the Lewis base were observed, suggesting that a decomposition product remains in the recycled ionic liquid. This effect could be minimized by acid washing the recycled ionic liquid prior to use. © Copyright by Kevin R. Caple January 24, 2014 All Rights Reserved Detailed Analysis of the Hydrogen Sulfide Production Step in a Sulfur-Sulfur Thermochemical Water Splitting Cycle Kevin R. Caple A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented January 24, 2014 Commencement June 2014 Doctor of Philosophy dissertation of Kevin R Caple presented on January 24, 2014 APPROVED: ________________________________________ Major Professor, representing Chemical Engineering ________________________________________ Head of the School of Chemical, Biological, and Environment Engineering ________________________________________ Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. __________________________________________________________________ Kevin R. Caple, Author ACKNOWLEDGEMENTS I would first like to acknowledge and thank the National Science Foundation who supplied financial support for this project. This material is based upon work supported by the National Science Foundation under Grant No. 0748280 I would like to thank my advisor, Dr. Alex Yokochi, who took me on as a fresh faced graduate student with no engineering background. Through his patience, teaching, time, and effort, he has allowed me to grow as an engineer, a researcher, and a person. I seek to emulate his enthusiasm and optimism towards his professional career as I begin my own and I will be forever thankful for allowing my pursuit of interests outside of the academic setting and focusing on living a balanced and full life. My graduate committee has been extremely helpful during my time here at Oregon State. I have had close interaction with Dr. Goran Jovanovic both in class and my research activities, from my Master’s degree to this PhD. I have taken classes from Drs. Chih-Hung Change and Greg Herman, as well as my Graduate Council Representative, Dr. John Conley. I would like to make special mention of the influence of Dr. Greg Rorrer during my time here at Oregon State. Through the undergraduate and graduate classes I took from him, to working closely with him as a teaching assistant, and him offering me a teaching position over the summer of 2013, he has shown the highest level of professionalism and work ethic that I would strive to model myself after. I would like to acknowledge my labmates in the Yokochi lab: Alex Bistrika, Malachi Bunn, Peter Kreider, Omar Muhammed, Yu Miao, Travis Campbell, Justin Pommerenck, Matt Delaney, and Nathan Coussens. I would like to especially thank Nick Auyeung for his initial work on this project and taking the time to bring me up to speed on that work before he graduated. I’d also like to thank Jeremy Campbell as a sounding board, compatriot, and friend throughout our time in the corner of the graduate offices in Gleeson. Thanks also go to Andy Brickman and Manfred Dittrich for their assistance with the development of any task that I needed, whether it be machining a new part, or finding the right tool for the job. I would like to thank my parents and older brother Ryan for their unquestioned support during my time as a graduate student here at OSU. My parents instilled in me the principles of hard work, discipline, and not taking anything too seriously while always supporting the professional decisions that I have made. Most importantly, I would like to thank my wife, Ratih Lusianti. As we navigated the difficult world of our PhD’s together, she provided me with support, a professional opinion that I could always ask advice of, a person that I was happy to go home with every day, and a loving home. I would not have been able to complete my PhD without her. A final thanks to Layla, whose happy face and wagging tail always lifted my spirits when it was needed TABLE OF CONTENTS Page 1. Introduction………………………………………………………………………………………………. 1 1.1. Background……………………………………………………………………………… 1 1.1.1. Objectives……………………………………………………………………. 4 1.2. Literature Review……………………………………………………………………. 4 1.2.1. Thermochemical cycles……………………………………………….. 4 1.2.1.1. Initial Development……………………………… 4 1.2.1.2. Metal/Metal Oxide Thermochemical Cycles…………………………………………………… 5 1.2.1.3. Metal Halide Thermochemical Cycles………………………………………………….. 7 1.2.1.4. Hybrid Sulfur and Mark 13 Thermochemical Cycles…………………………………………………. 10 1.2.1.5. The Sulfur-Iodine Thermochemical Cycle……………………………………………………. 11 1.2.2. Exergetic Efficiency…………………………………………………….. 17 1.2.3. Ionic Liquids and Alternative Reaction Media…………….. 21 1.2.3.1. Ionic Liquids………………………………………… 21 1.2.3.2. Alternative Reaction Media…………………. 22 1.2.4. Summary of Previous work on Sulfur-Sulfur Cycle………. 23 2. Exergetic Efficiency………………………………………………………………………………….. 29 2.1. Analysis…………………………………………………………………………………… 30 2.2. Results and Discussion…………………………………………………………….. 33 2.3. Conclusions……………………………………………………………………………… 38 3. Experimental Results and Discussion…………………………………………………..……. 40 3.1. “Standard” Reaction Conditions………………………………………………. 40 TABLE OF CONTENTS (continued) Page 3.1.1. Materials and Methods…………………………………….………….. 40 3.1.2. Results and Discussion…………………………………………………. 42 3.2. Iodine Recovery…………………………………………………………..…………… 48 3.2.1. Materials and Methods…………………………………..…………….. 49 3.2.2. Results and Discussion………………………………………………… 49 3.3. Effect of Water on Kinetics…………………………………………………….. 51 3.3.1. Materials
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